How to Correctly Use runOnUiThread to Update Android UI from a Background Thread?

runOnUiThread in Android Development

Threads in Android are essential for performing tasks in the background without blocking the main UI thread. To interact with UI elements from a background thread, Android provides the runOnUiThread method.

Misunderstanding in the Provided Code

In the given code, the issue arises within the runThread method. Creating a new Thread instance with the Runnable implementation is correct. However, executing runOnUiThread directly within the background thread is incorrect.

Correct Implementation

To use runOnUiThread properly, the recommended approach is to create a separate Runnable object inside the background thread and then pass it to runOnUiThread. The main UI thread will then execute this passed Runnable to update the UI elements.

Here is the corrected code for the runThread method:

private void runThread() {
    new Thread() {
        public void run() {
            while (i++ < 1000) {
                try {
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            btn.setText("#" + i);
                        }
                    });
                    Thread.sleep(300);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }.start();
}

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